S127: Hydrogen production by direct fermentation of corn stover using a consortium of Clostridium microbes

When produced from waste lignocellulosic materials, hydrogen fuel is one of the most promising options for a long-term, net-zero emission energy carrier.  The most significant barrier to industrial scale production of bio-H₂ is the ability to produce the gas economically.  Advances in consolidated bioprocessing are required to improve the rates of cellulose hydrolysis and its subsequent fermentation. Clostridium thermocellum is a thermophilic, anaerobic microbe with the highest known rate of cellulose degradation. Although it contains hemicellulases it is only capable of metabolizing the cellulose fraction of lignocellulosic materials. The goal of this study was to completely utilize the carbohydrate portion of the substrate, producing an overall higher yield of hydrogen.  Reactor parameters and substrate loading were first optimized using C. thermocellum grown on avicel and pretreated cornstover at 1, 2.5 and 5 g/L. An increase in carbon loading resulted in an increase in the maximum H₂ production rates and a decrease in the overall H₂ yield in both substrates. Milled corn stover was then fermented in a co-culture with C. thermocellum and a pentose-degrading clostridium consortium isolated from heat-treated sewage sludge. Initial data show that C. thermocellum is able to metabolize the cellulose fraction of milled cornstover, while hydrolyzing hemicellulose to xylose and arabinose.  The consortium is then able to ferment the pentose sugars for additional H₂ production. The H₂, organic acids and ethanol produced by the co-culture is greater than with C. thermocellum alone, which is consistent with the more complete utilization of lignocellulose sugars in the co-culture fermentation.